He had to exteriorize his archetype
“For the alchemist it was clear that the “centre,” or what we would call the self, does not lie in the ego but is outside it, “in us” yet not “in our mind,” being located rather in that which we unconsciously are, the “quid” which we still have to recognize.
Today we would call it the unconscious, and we distinguish between a personal unconscious which enables us to recognize the shadow and an impersonal unconscious which enables us to recognize the archetypal symbol of the self.
Such a point of view was inaccessible to the alchemist, and having no idea of the theory of knowledge, he had to exteriorize his archetype in the traditional way and lodge it in matter, even though he felt, as Dorn and others undoubtedly did, that the center was paradoxically in man and yet at the same time outside him.” ~Carl Jung, Aion, Page 169